Cellular products such as sheets and tubes of expanded blends of polyvinyl chloride resin and certain rubbers have achieved wide use as insulating materials, particularly for pipe insulation.
Expansible blends of polyvinyl chloride resin and certain rubbers that provide foamed products having a closed cell system are described in, for example, U.S. Pat. Nos. 2,849,028 and 4,245,055. In general, the aforementioned patents disclose a method of incorporating a blowing agent into a foamable resin/rubber blend which can be heated to decompose the blowing agent and thereby provide an expanded cellular object without the use of any forming molds. For instance, U.S. Pat. No. 2,849,028 discloses blends of polyvinyl chloride resin and butadiene-acrylonitrile copolymer rubber that are freely expanded at a temperature of about 300.degree. F. to provide cellular products useful for pipe insulation. U.S. Pat. No. 4,245,055 discloses similarly prepared cellular products prepared from a blend which includes polymethylmethacrylate.